Dr. Ahmed G. Abo-Khalil

Electrical Engineering Department

Amplitude

Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation. If a variable undergoes regular oscillations,
and a graph of the system is drawn with the oscillating variable as the
vertical axis and time as the horizontal axis, the amplitude is visually
represented by the vertical distance between the extrema of the curve and the equilibrium value.

Peak-to-peak amplitude

Peak-to-peak amplitude is the change between peak (highest amplitude value) and trough (lowest amplitude value, which can be negative). With appropriate
circuitry, peak-to-peak amplitudes can be measured by meters or by
viewing the waveform on an oscilloscope.
Peak-to-peak is a straightforward measurement on an oscilloscope, the
peaks of the waveform being easily identified and measured against the graticule. This remains a common way of specifying amplitude, but sometimes other measures of amplitude are more appropriate.

Semi-amplitude

Semi-amplitude means half the peak-to-peak amplitude. It is the most widely used measure of orbital amplitude in astronomy and the measurement of small semi-amplitudes of nearby stars is important in the search for exoplanets. For a sine wave, peak amplitude and semi-amplitude are the same.

Some scientists use "amplitude" or "peak amplitude" to mean semi-amplitude, that is, half the peak-to-peak amplitude.[